Circuit arrangement for electrical time control



Nov. 17, 1936. A. w. VINGERHOETS 2,061,011

CIRCUIT ARRANGEMENT FOR ELECTRICAL TIME CONTROL Filed July 10, 1933 2Sheets-$heet 1 Inven ror ANTONIUS WILHELMUJ VINGERHOET5 A Home;

Nov. 17, 1936. A. w. VINGERHOETS 2,061,011

CIRCUIT ARRANGEMENT FOR ELECTRICAL TIME CONTROL Filed July 10, 193328heets-Sheet 2 Invenfor ANTON/US 'WILHELMUJ V/NGERHOETJ Afforn e]Patented Nov. 17, 1936 PATENT OFFICE cmoo'rr aamcsmr roa ELECTRICAL rmsCONTROL Antonius Wilhehnns Vlnzerhoets, Eindhoven,

Netherlands, signer, by meme assignments, to N. V. PhilipsGloeilampenfabrieken, Eindhoven, Netherlands, a Dutch companyApplication July 10, 1933, Serial No. 879,311 In Germany July 1932 13Claims. '(Cl. 250-27) My invention relates to novel circuit arrangementsfor electrical time control.

My invention broadly applies to circuit arrangements for the electricalcontrol of the duration of processes, and is specially adapted for suchcontrol of processes of very short duration.

A special and important application of my invention is in connectionwith X-ray installations, and specially with short time radiographicexposures, and I shall describe my invention primarily in connectionwith such use. However, it should be well understood that manifold otherapplications of my invention may suggest themselves. My invention can beused irrespective whether the process, the duration oi which is to becontrolled, is an electrical, other physical, chemical, or other kind ofprocess for example in electric signaling devices, in makingphotographic prints from negative images, in electrical therapy, etc.

Various means have been suggested for the control of the duration ofshort time processes and ,also in connection with the taking of shorttime X-ray exposures. Clock switches, tor instance, have been widelyused. Suohswitches after a given time interval may act on a relay orotherwise make or break electrical circuits. Clock switches have,however, various disadvantages, among others, they require the windingof springs, are comparatively expensive, etc.

In view of the inherent drawbacks of such clock switches, various othertime control means have been already suggested.

For instance, in "U. S. Patent 1,819,999 to Kears= ley, a timing devicehas been suggested in which a three electrode tube is used as the timecontrol means, in which tube the grid potential m varied in accordancewith the change of voltage of a previously charged condenser.

The potential of the grid thereby varies according to an exponentialfunction between two values, which are so selected that at one value acurrent may flow through the tube, whereas at the other value thecurrent is suppressed.

The above arrangement has, however. serious drawbacks. As thisarrangement requires the pro-charging oi the condenser, in alternatingcurrent installation, when the discharge initiated, the condenserisliable to. lose part of its charge before the alternating anode-voltagehas assumed a suiliciently high value to effect the discharge throughthe tube. This requires the use of auxiliary control means, to insurethat the discharge of the condenser may only start at a moment when'theanode voltage has assumed a sulficiently positive value.

A further disadvantage is that with the above arrangement specialprovisions have to be taken to prevent the discharge of the condenserthrough the grid oi the tube.

also, the arrangement requires the charging of the condenser every timeprior to the use of the device, which consumes considerable time in viewof the pulsating character of the rectified current used for thispurpose and the electrical constants of the charging circuit.

The present invention relates to an arrangement in which all of theabove drawbacks are avoided and which arrangement has further importantadvantages.

According to the invention the potential of a condenser during itscharging is used to influence the potential of the auxiliary electrodeor grid of a three-electrode discharge tube.

Furthermore, by using the same alternating current source both for theanode voltage of the tubes as well as for the charging of the condenserthrough a rectifier, and by providing for the proper phase-connections,it is possible accord ing to the invention to have the starting oi thecharging oi. the condenser automatically coincide with the starting of apositive half-wave oi the anode voltage.

Various embodiments of my invention are possible. For instance anarrangement can be provided in winch the condenser is charged through aresistance which is connected tothe grid of the discharge tube andaffects the potential of same in such a manner that the decreasingvoltage drop in the resistance during the charging of the con denseraffects the bias of the grid. For instance,

while the charging current is high and the voltage drop in theresistance large, this large voltage drop negatively biases the grid,thereby block ing the discharge current through the tube. As thecondenser gradually charges, the voltage drop in the resistancedecreases and the grid bias increases until finally a value is obtainedat which the discharge through the tube is established. 0r inversely thevoltage drop in the resistance may apply a positive bias to the tubewhich sets in the discharge and the charging of the condenser graduallydecreases this positive bias until the current through the tube isblocked.

Again in another embodiment of my invention,'

the potential variations of the charging condenser may he used todirectly control the biasing oi the grid of the discharge tube in asomewhat similar manner.

In the first case it is necemary, in the second case it is advantageousto so interconnect the alternating current which supplies the anodepotential for the discharge tube and the alternating current used forthe charging of the condenser through a half-wave rectifier, that theoperative half-waves of the charging current coincide with the positivehalf-waves of the charging current. Thus the charging of the condenseralways starts at the right moment, namely, at that instant when theanode voltage enters its positive or operative phase.

Preferably the same transformer Winding'is used'to supply the anodecurrent as well as the charging current.

Usually I provide a switch in the circuit arrangement by means of whichthe condenser is normally short-circuited and which switch in anotherposition closes the charging circuit of the condenser. It should benoted that the discharge of the condenser consumes practically no time,as the condenser is directly short-circuited and thus the device is welladapted for quick repeated use.

The invention will be more fully described with reference to theaccompanying drawings showing arrangements illustrating variousembodiments of my invention and in which:

Figure l is a diagram of an arrangement in which the discharge tube actsas a relay through which normally the current flows, the current beinginterrupted to control the duration of the process to be controlled andto achieve this the bias of the grid is varied by the voltage drop in aresistance which is connected in series with the charging condenser.

Figs. 2, 3, 4 and 5, show various modifications of my invention, inwhich the current through the discharge tube is normally suppressed andis only permitted to flow during the control time interval, the bias forthe grid being directly af fected by the voltage of the chargingcondenser.

Referring to Figure 1, a discharge tube I is provided which acts as arelay and which cominterrupt the current through the tube.

prises an incandescible cathode 2, an auxiliary electrode or grid 3 andan anode l.

The discharge tube I, is preferably a gasfilled arc-discharge tube,although a, highvacuum tube may be also employed which, however, shouldbe operated preferably at saturation voltage. As a rule, I prefer to usegas-filled tubes, as high vacuum tubes have the drawback that theiranode current varies with the potential applied to the grid.

As is known, as long as the anode potential has a constant value in anarc discharge tube, limited variations of the grid potential do notHowever, if the anode voltage is an alternating voltage, the arc isinterrupted in. each half-wave, and re-ignition of the arc depends onthe potential applied to the grid. If during a positive halfwave thepotential of the grid is sufliciently high, the tube is ignited and thefull current permitted to pass. Thereby, the voltage drop in the tube isof no importance. However, if during a positive half -wave the potentialof the auxiliary electrode is but slightly less than that required forthe ignition of the tube, the current is altogether interrupted or atleast practically suppressed.

A transformer is provided for the energy supply of the arrangement, theprimary winding I2 of which is connected to the supply of alternatingcurrent, and which transformer has two secondary windings I3 and I4.

The winding I3 supplies the voltage for the anode circuit of the tube Iand is connected with its two end terminals 30 and 3i across thiscircuit. The winding I3 is also provided with two intermediate taps 32and 33.

Across the portion 36 to 32 of the winding I3 is connected theincandescible cathode 2 of the tube I.

The anode circuit of the discharge tube I comprises a magnet coil I, thearmature of which actuates a. contact 8, which serves for either theclosing or the opening of a circuit to be controlled, marked X,whichcircuit in turn controls the process, the duration of which it isdesired to control. If this process is an X-ray exposure. the contact 6may serve to close the primary circuit of the high voltage transformerof the X- ray tube. In Fig. 1, the relay 1 is shown as normallyenergized and the contact 8 normally open, this contact being closedupon the deenergization of the magnet coil 1.

A condenser 5 is provided with one of its electrodes, which as willappear is the negative electrode, in permanent electrical connection at36 with the grid 3. The other electrode of the condenser 5 is connectedto the heel 34 of a twoposition switch I5, the free end of which switchmay be brought into contact with either one of the contacts marked I andII, these switch positions being hereafter referred to as positions Iand II respectively.

The contact I is connected to the point 36, and while the switch I5 isin position I, the condenser is short-circuited.

When the switch I5 is moved into position II. the charging circuit ofthe condenser 6 is established. This circuit comprises a half-waverectifier tube 9-having an incandescible cathode I0 and an anode II-thetransformer winding I4, a variable resistance 6, and the condenser 5.

The cathode III of the rectifier 9 is heated from a tapped portion ofthe winding I4.

Upon closure of the charging circuit, the condenser is gradually chargedup by the rectified current, the charging time depending on theelectrical constants of the circuit and may be adjusted by varying theresistance 6.

The Junction point 36 of the resistance 6 and of the winding I4, isconnected to the tap 33 of the transformer winding I3, thus to a pointthe potential of which lies between that of the anode and that of thecathode; the other end of the resistance 6 is connected to the junctionpoint 36 and is thus also connected to the auxiliary electrode 3. Itwill thus appear that while the condenser charges the potential of theauxiliary electrode is rendered less positive, by the extent of thevoltage drop in the resistance 6.

As long as the charging circuit is open, the potential of the auxiliaryelectrode 3 is willciently high to provide for the ignition of tube Iduring each positive half-wave of its anode voltage.

When the charging circuit is closed, provided the arrangement andconnections of the windings are such that the operating half-waves orcurrent flow through the charging circuit coincides with the positivehalf-waves of the anode voltage of tube I, the potential of theauxiliary electrode will be decreased below the value required for theignition of the tube I.

This interrupts the current flow in the anode circuit and deenergizesthe magnet I, which in the arrangement shown then will cause the contact8 to close the circuit X controlled by same.

However, with the gradual charging of the condenser 5, the voltage dropin the resistance 6 the auxiliary electrode again assumes a sum-'decreases and the extent'by which this voltage drop reduces thepotential of the auxiliary electrode gradually diminishes. After a giventime interval, the value of which can be adjusted with great precisionand in a simple manner by the proper adjustment of the variableresistance 6,

c'iently positive potential to allow the ignition of the tube I.

The current flow through the anode circuit is thereby reestablished, themagnet coil 1 reenergized and the contact 8 opened.

It is evident that the energization of magnet coil 1 instead of beingused to eflect the opening of the contact 8, can be used in an analogousmanner to eiIect the closure of a similar circuit control contact.

For the proper adjustment of the duration of the suppression of theanode current, and thus of the closure or opening of the contact 8,besides making the resistance' variable, the capacity of the condensermay also be made adjustable, which makes it possible to obtain a veryfine adjustment. Such a circuit arrangement is therefore exceedinglywell suited for a time switch for X-ray installations, especially fortaking exposures of very short duration, in which case the exactadjustment of the exposure time isof very great importance.

It should be, of course, understood that the magnet switch 1-4 has to beof such character as to respond to the pulsatory current passing throughthe anode circuit.

Between successive uses, the switch I5 is placed in the position 1,whereby the condenser 5 is short-circuited and loses its charge almostinstantaneously.

Insteadof providing a separate transformer winding to supply thecharging current, it is also possible to use for this purpose the samewinding which feeds the anodeeircuit of the tube I. This is illustratedin Fig. 2, the arrangement of which, however, differs from that of Fig.1, also in several other respects. While in the arrangement of Fig. 1,the anode circuit I is energized all the time except when suppressedduring the charging of the condenser and thus the tube I actsas anormally energized or closed circuit relay, in the arrangement of Fig.2, the current through tube I is always suppressed except for theduration of the charging of the condenser, thus the tube operates as anormally deenerglzed or "open circuit" relay.

While the discharge circuit of the condenser E and the connections tothe junction point" are unaltered in Fig. 2, the other end of theresistance 6 instead of being connected to an intermediate tap of thesecondary transformer winding IS-which in this case feeds both the anodecircuit of tube I as well as the charging circuitis connected to theanode II of the rectifier tube 9. The cathode III of the tube 9 isconnected to the end terminal 40 of the winding I6, close to which a tap4| is provided, the portion 40 to H of the winding supplying the heatingcurrent for the rectifier cathode I0.

The winding It is furthermore provided with two closely spaced taps l2and ll, which supply the heating current for the cathode 2 of tube I,the tap 42 also serving as the cathode terminal of the anode circuit.

Furthermore, between the tap it and the terminal N of winding it, thereis provided a tap II, or to permit adjustment of the voltage pref- -thepotential of the cathode tap 42.

erably a plurality of taps-the tap I1 being connected to the contact IIof the charging circuit.

grid 3, with which it is in electrical connection,

a charge which gives the grid a negative bias with respect to itscathode 2. As a result, the anode current through the tube I is blocked.

The charging circuit goes through winding I6, rectifier 9, resistance i,condenser 5, switch I5, contact 11, and tap II. It will be noted thatin' this arrangement the rectifier is connected to a point of the,winding, the potential of which is further away from that of the anode4 than is Thus the charging circuit and the anode circuit are in phaseopposition.

When the switch I5 is brought in position II, a voltage is applied tothe grid 3, which corresponds to the voltage induced in the windingportion 42-I| and which in the operative haliwave of the anode voltageincreases the grid potential above the ignition value. However, as thecondenser charges, the potential applied to the grid 3 is graduallyreduced, and in a predetermined time interval the grid potential fallsbelow the value required to permit the ignition of the tube. Thus theanode current is interrupted and the contact 8 is actuated.

In this arrangement, the negative electrode of the condenser isconnected to the auxiliary elec-' trode 3, the potential thereof beingthus directly dependent on the condenser voltage.

It should be noted that the duration of the current through the anodecircuit of tube I is not affected by the instantaneous value of theanode voltage at which the switch I5 closes the charging circuit, as thecharging of the condenser can only start in the operative half cycle ofthe anode potential.

The proper adjustment for the duration of the anode current can beobtained by either the adjustment of the resistance 6, or that of thecondenser 5 or of the tap II or by a combination of these adjustments.

In'the arrangement of Fig. 2, if energization of coil I should cause theclosure of contact 8, a biasing spring 45 serves to hold the contact 8normally open. When the coil I is energized, the pull of the magnetovercomes the spring 45 and the contact 8 is closed.

Figure 3 shows a further modification of my invention, which gives anarrangement similar to that of Fig. 2 except for the provision of athreeposition instead of a two-position switch and the addition of aresistance 20 connected across a portion of the winding I6.

The switch l8 contacts with a segment I9 in the positions I and III, thesegment Iii being connected to the junction point 35. In position I, theswitch short-circuits the condenser 5 in the same manner as in theprevious figures.

In position II, the switch establishes the charging circuit of thecondenser in the same manner as in Fig. 2, except that contact IIinstead of being connected to a tap of the winding I6 is vides for amore convenient variation of the bias voltage to be applied to grid 3.

Preferably, the resistance 20 is shunted across a portion oi the windingl6, which portion extends on both sides of the taps 42 and 42 for thecathode 2. Thereby, it is made possible, to better adapt the biasvoltage to the characteristic of the tube I, and it required, the tubemay be operated without grid bias, or with negative grid bias.

In the position III, the condenser remains short-circuited, but thecontact III, being connected to the movable contact 2|, the grid is keptcontinuously at a sufllciently high potential to maintain the ignitionof tube l. Thus, a current is maintained in the anode circuit as long asthe switch is kept in position III.

The arrangement shown in Fig. 3 thus permits to eil'ect either a shorttime control of predetermined duration or may perpetuate a desiredcondition. For instance, when applied to X-ray installations, thearrangement may be used both for short radiographic exposures and forcontinuous fluoroscopic work. In such case, I prefer to combine with theswitch ll other regulating means which upon movement of the switch intothe positions II and III respectively, cause the establishing of theproper 'voltage and current values of the X-ray for radiographic andfluoroscopic work respectively.

The arrangement of Fig. 4 is similar to that oi Fig. 2, except for thefollowing. A separate winding 22 is used ior'the heating of the cathode2 oi tube I, the contact 11 is connected to the winding 22 instead of tothe tap l1, whereas the latter is connected to the heel 34 of the switchii.

In this arrangement, the anode circuit oi tube l is altogetherinterrupted, until the charging circuit is closed when the switch I!takes the position II. This arrangement has the advantage that undesiredignition of the relay tube i is avoided even if-due to someuncontrollable circumstances, for instance, due to extraneous reasons-ahigh voltage impulse is induced in the anode circuit which otherwisemight ignite the tube in spite of the sub-ignition potential applied tothe grid.

In this arrangement the charging of the condenser starts as soon as theswitch leaves the contact I, whereas the anode circuit only closes whenthe switch has contacted with II.

In the arrangement of the Figures 2 to 4 the drawback may occur that theend of the time interval during which the switch I should remain closedis not exactly defined and that current impulses which, due to the lowergrid potential, start at a later phase, become transitory, so that theswitch 8 instead of being positively actuated is caused to chatter overa plurality of cycles.

This drawback is entirely avoided and the advantages of the arrangement01 Fig. 4 maintained by the arrangement shown in Fig. 5.

In this arrangement, the cathode 2 is again connected to the winding l6,whereas the electrode oi the condenser 5 is connected to the tap i1,similarly to Fig. 4.

The switch I5 is omitted, and the armature of magnet coil I is providedwith two additional contacts 23 and 24. Furthermore, there is providedin the anode circuit a manually operable switch 25. The contact 23 isadapted to shortcircuit the condenser 5, whereas the contact 24 is inmultiple with the switch 25 and serves as a stick contact for the magnetI.

- As long as the switch 25 is kept open the anode circuit is interruptedand the spring biased armature of magnet coil I is in its upperposition, whereby contact 22 short-circuits the condenser, whereascontacts 24 and I are open.

When switch 25 is closed, the anode circuit is immediately establishedas the grid 3 assumes simultaneously with anode 4 a positive potential,coil 1 is now energized and breaks contact 23 and makes contact 24 and8. The switch 25 may be now released as contact 24 retains the anodecircuit closed.

The condenser 5 being no more short-circuited charges up in the samemanner as described in connection with Fig. 2 and after having chargedto a given value causes a drop of the grid potential, therebyinterrupting the anode current and deenergizing the relay coil I. Oncethe anode current is interrupted the magnet I cannot be re-energized andthe chattering of the contact 4 is thus prevented.

It should be noted that in this arrangement the short-circuiting anddischarging of the condenser takes place automatically.

To insure that the contact 24 be closed before the manual switch 25 isopened, the later is preferably designed as an automatically openingswitch provided with sufllcient delay to insure the closure of the anodecircuit until the magnet coil 1 has attracted its armature.

The automatic opening of the switch 25 is also desirable to prevent theprolonged closure of this switch which otherwise might again causechattering of contact 4, due to the fact that after the magnetcontrolled switch has returned 'to its normal position and the condenserpartly discharged closure of the switch 25 would re-establish the anodecurrent.

In a specific embodiment used for controlling X-ray exposures, where therelay contact 24 required .05 second for its closure (after the switch25 has been closed) and with a required minimum exposure time of .1second, the automatic closure time of the switch 25 was selected to be.07 second. Or generally the time of closure effected by the switch 25has to be larger than the time required for the closure of switch 24 andsmaller than the minimum time during which the condition effected bycontact 8 should persist.

As there are various known switch constructions suitable for thispurpose and no novelty is claimed for this switch per se, its detaileddescription and illustration is not believed to be necessary.

It might be mentioned that a suitable construction for this switch isthe one used in automatic telephone apparatus, which comprises a rotarydisc which upon manual displacement is returned by a biasing spring at afixed speed and during such return establishes and breaks certaincircuit connections.

As stated, instead oi using a gas-filled discharge tube for the relaytube I, a high vacuum electron discharge tube may be used. In this case,the lowering of the grid potential instead of suppressing the ignitionof the discharge tube, cuts oil the current flow through the tube.

While I have described my invention in connection with certainembodiments and in certain applications, I do not wish to be limited tosuch embodiments and applications, but desire the appended claims to beconstrued as broadly as permissible in view of the prior art.

What I claim is:

- 1. A circuit arrangement for automatically with said auxiliaryelectrode, a transformer winding to supply the current to the tubecircult and to the charging circuit, a potentiometer connected across aportion of said winding and a switching device to connect the movablecontact of said potentiometer to the other electrode of the condenserfor the charging of said condenser.

2. A circuit arrangement for automatically limiting the duration 01' anelectrically controlled process, comprising a discharge tube having acathode, an anode and an auxiliary electrode, an anode circuit for saiddischarge tube and an alternating current supply for said circuit, acondenser and a charging circuit for same, means to apply a potential tothe grid which is sumcientlyhigh to permit the current flow through saidanode circuit during the positive half-wave of said alternating current,and a three-position switch which in one of its positions shortcircuitssaid condenser and in its second position applies said potential to theauxiliary electrode, and in its third position shortcircuits saidcondenser and simultaneously applies said potential to the auxiliaryelectrode.

3. A circuit arrangement for automatically limiting the duration of anelectrically-controlled process, comprising an arc discharge tube havinga cathode, an anode, and an auxiliary electrode, a condenser and acharging circuit therefor, an anode circuit for said discharge tubeincluding electro-responsive means, and a twoposition switching devicehaving a normal position in which it interrupts the anode circuit at apoint outside the tube and a second position in which it establishessaid anode circuit and initiates charging of said condenser, saidcondenser during the charging thereof impressing upon said auxiliaryelectrode a varying potential which after a predetermined time intervalassumes a value at which current in the anode circuit is suppressed andsaid electro-responsive means is deenergized to cause interruption ofthe process.

4. A circuit arrangement for switching on an electric current andautomatically limiting the duration thereof, comprising a transformerhaving a primary winding, a secondary winding and a tertiary winding, agas-filled electric discharge tube having a filamentary cathode, ananode and an auxiliary electrode adapted to control the starting of thedischarge of the said tube, said cathode being connected to saidtertiary winding so as to be energized thereby, a second discharge tubehaving a filamentary. cathode which is energized from a portion oi! saidsecondary winding and an anode, a variable resistance connecting saidlatter anode. and said auxiliary electrode, an electromagnetica iyactuated relay switch having a magnet coil, the anode of said firstdischarge tube being connected through said coil to said secondarywinding, said secondary winding having an intermediate tap between theconnection to the anode of said first discharge tube and the connectionto the cathode of said second discharge tube and a condenser connectedbetween said auxiliary electrode and said tap, a two-way switchconnecting said tap in one position to the cathode of said firstdischarge tube and in a second position to said auxiliary electrode,thereby short circuiting said condenser.

5. A circuit arrangement for switching on an electric current during apredetermined time, comprising a transformer having a primary wind ing,a gas-filled electric discharge tube having a filamentary cathode, ananode and an auxiliary electrode adapted to control the starting of thedischarge in saidtube, said cathode being connected over a portion ofsaid secondary winding so as to be energized therefrom, a relay switchactuated by a magnet coil which is connected in series with a manuallyactuated switch between said anode and one point of said secondarywinding, a tap intermediate between said point and said portion of thesecondary winding and a condenser connected between said tap and saidauxiliary electrode, said auxiliary electrode being further connectedthrough a variable resistance and a second electric discharge tubehaving an anode and a filamentary cathode to a point of said secondarywinding in opposite phase as said first point oi. this winding withrespect to the portion energizing the cathode of said first tube, saidsecond discharge tubebeing connected with its anode turned to theauxiliary electrode of said first tube and its cathode turned to thesecondary winding, said relay switch comprising three circuit breakersone of which is normally closed and short-circuits said condenser, thesecond of which is normally open and forms a stick contact for the saidcoil and the third of which controls the current to be switched on bythe circuit arrangement during a predetermined time.

6. In a timing device, an arc discharge tube having an anode, a cathodeand a control electrode, a normally open anode circuit for said tube,means to gradually vary the control electrode potential from a definitevalue which is positive with respect to the cathode and makes the tubeconductive to a lower value which makes the tube non-conductive, saidmeans comprising an electrical condenser and a normally inoperativecharging circuit therefor, and switching means connected to said twocircuits to simultaneously switch on the charging current through saidcondenser and close the anode circuit at a point outside the dischargetube. a

'7. In a timing device, an arc discharge tube having an anode, a cathodeand a control electrode, an anode circuit for said tube having aninterruption outside said tube, 'a second circuit comprising anelectrical condenser and means to normally maintain saidcondenserdischarged, a transformer winding common to said two circults and havinga variable intermediate tap, a

rectifier in said second circuit having its negative side connected tosaid winding on one side of control electrode in said path, a condenserhaving one electrode connected to said control electrode, an anodecircuit for said tube including the discharge path and currentresponsive means, a charging circuit for said condenser and includingsame, a heating current circuit for energizing said cathode andincluding same, said circuits having common portions, and switchingmeans connected to said charging circuit and to a point of said anodecircuit outside said discharge path to selectively make said chargingcircuit operative or inoperative and to establish said anode circuitwhensaid charging circuit is made operative. 9. In combination, anelectric discharge device having an anode, a cathode and a controlelectrode, means for supplying anode current to said tube, means forapplying to the control electrode a potential of such value as to rendersaid discharge device normally conductive, means comprising a condenserto vary the potential of said control electrode between said value and asecond value at which the tube is non-conductive, and means forswitching on the condenser to gradually change the potential oi! thecontrol electrode from the first value to the second value and forsimultaneously establishing the connections to permit the flow o! anodecurrent.

10. In combination an electric discharge device having an anode, acathode and a control electrode, a rectifier having a cathode and ananode, a series circuit including said condenser and said rectifier, apoint in said circuit between said condenser and said rectifier beingconnected to said control electrode, means for supplying an alternatingelectromotive force to said circuit and between the anode and cathode ofsaid discharge device, and a circuit arrangement including atwo-position switching device, said switch in one position permittingthe application oi! electromotive iorce to said rectifier and condenserand between the anode and cathode of said discharge device, saidswitching device in its other position preventing the application ofelectromotive force to said condenser and between the anode andcathodeof said discharge tube.

11. In a timing device an arc discharge tube having an anode, a cathodeand a control electrode, a transformer winding having an intermediatetap, an anode circuit for said tube comprising a magnetic relay coil anda portion of said winding to one side of said tap, a series circuitcomprising a rectifier, a variable resistance,

a condenser, and a portion of said winding at the other side 0! saidtap, and a two-position switch included in the connection from thecathode of the tube to said winding, said switch in one positionestablishing said anode circuit and in the other position interruptingthe anode circuit at a point outside the discharge tube andshortcircuiting said condenser.

12. In a timing device, an arc discharge tube anode of said tube and apoint on said winding at the other side of said tap, and a two-positionswitching device which in one position connects said tap to said cathodeto establish the anode circuit of said tube and in its other positiondisconnects the tap from the cathode to interrupt the anode circuit andconnects same to the control electrode to short-circuit the condenser.

13. In a timing device, an arc discharge tube having an anode, a cathodeand a control electrode, a source of alternating current comprising awinding having an intermediate tap, a condenser connected between saidcontrol electrode and said tap, a rectifier having an anode connectedthrough a resistance to said control electrode and a cathode, an opencircuit relay switch having a coil connected with one end to a point onsaid winding on the other side of said tap and with its other endconnected through said switch to the anode of said are discharge tube, asecond switch connected in multiple with said condenser andinterconnected with said first switch, said second switch being closedwhen saidfirst switch is open and being open when said first switch isclosed, and an auxiliary switch connected in parallel with said firstswitch.

ANTONIUS WILHELMUS VINGERHOEIS.

